Unsaturated oil and fatty acid have been widely used in the coating industry due to the ability of air oxidative crosslinking to form a crosslinked coating polymer. This chemistry has also been used to modify urethane to make oil-modified urethanes (OMU) and alkyd modified urethanes (uralkyd). The major advantages of the OMU and uralkyd coatings include one package stable systems. It has been known that OMU and uralkyd coatings exhibit excellent resistance to abrasion, chemicals and solvents. Conventional OMUs or uralkyds prepared in organic solvent are relatively low molecular weight polymers. The low molecular weight polymers are formulated with metallic driers that function as crosslinking catalysts. When these formulated polymers are applied as clear or pigmented coatings to a surface, the organic solvent evaporates and the film is crosslinked by air oxidation at room temperature through the ethylenic unsaturation in the oil or fatty acid to form a tough, crosslinked polymer film. The coating mixtures are stable in the absence of air or oxygen. These characteristics have made the solvent-based OMU and uralkyd widely used for wood floor coatings and trim varnishes for many years.
There has been regulatory pressure to reduce the volatile organic compound (VOC) emissions from coatings due to the use of organic solvents. One of the common methods used to reduce the VOCs is to increase the solids content of the coating materials. To maintain the rheological properties of higher solids content oil-modified urethanes at the same levels as the lower solids content oil-modified urethanes, the molecular weight of the oil-modified urethanes is decreased. In general, matching the overall performance of higher molecular weight polymers using a lower molecular weight polymer is difficult. There are drawbacks of the lower molecular weight oil-modified urethanes which include a longer drying time and a softer polymer film.
Polyurethanes formed by the reaction of isocyanates with polyols can be used for coating materials. Coatings from polyurethanes usually have good resistance to abrasion and chemicals, along with some flexibility and hardness. Although polymers in polyurethane coatings can have high molecular weights, such as urethane lacquers and polyurethane dispersions, many of the polymers used in urethane coatings are oligomers, which have low molecular weights. These low molecular weight urethanes may be cured or crosslinked during or after film formation. For instance, oil-modified urethane can be cured by air oxidation. Additionally, moisture-cured urethane can be cured by the reaction between isocyanate with moisture in air. Two-component urethane can be cured by the reaction between isocyanate groups with active hydrogen compound such as a hydroxyl or an amine. A radiation curable urethane can be cured by radiation in the presence of photo-initiator. Generally, problems exist with urethane lacquers as these lacquers do not have high solid content and good chemical resistance. Two-component and radiation curable urethanes have been found not to be convenient for use for consumers, as these along with isocyanate terminated moisture-cure urethanes are not very easy to handle. Thus, such coatings are not well suited for do-it-yourself wood coating applications.
The most widely used coating materials for wood floor do-it-yourself coatings remains solvent-based oil-modified urethane or urethane modified oil coatings. U.S. Pat. No. 2,970,062, for example, proposes to react drying or semi-drying vegetable oil with polyhydroxy alcohol to make a diol-ester intermediate. The resultant diol ester intermediate then reacts with a polyisocyanate at a controlled ratio in aromatic organic solvent. The final solvent-based oil-modified urethane is a stable system for coatings and adhesives. U.S. Pat. No. 3,022,326 proposes to incorporate 8-50% polyethylene or polypropylene glycol to urethane modified vegetable oil to make a solvent-based fast dry polymer film for coatings with improved flexibility. However, these and the oil-modified urethanes suggested in U.S. Pat. No. 2,970,062 are relatively low in non-volatile and high in viscosity, and are not suitable for low VOC coatings.
Government regulation, of volatile organic compounds in coating products mandates the reduction of the amount of organic solvent in the products. In the effort to reduce the amount of solvent, high solids oil-modified urethanes or uralkyds are being used. High solids oil modified urethane or uralkyds are achieved mainly by decreasing the molecular weight of the polymer or by the use of reactive diluents that may contain two or more functional groups per molecule that are capable of air oxidation. Crosslinking occurs between both the reactive diluent and the polymer itself. However, it is very difficult for the high solids oil-modified urethane or uralkyd to match the performance of the conventional one due to the slow dry and soft film. To overcome these problems, a second curing reaction is considered for introduction into high solids oil-modified urethane or uralkyd to make storage stable dual-cure urethanes.
U.S. Pat. No. 5,693,715 describes the polymerization of dicyclopentadiene and linseed oil to produce a linseed oil-cyclopentadiene copolymer. This copolymer can be used by itself as an air curable vehicle or blended with a second polymeric vehicle as a reactive diluent for coating binder. However, this product dries slowly.
U.S. Pat. No. 5,580,947 describes to the reaction of isophorone diisocyanate or other aliphatic diisocyanates with olefinically unsaturated carboxylic acid to make an amide containing oligomer for room temperature oxidative cure one-component coatings. These oligomers dry slowly.
U.S. Pat. Nos. 4,067,844; 4,222,925; 4,374,237; 4,687,533; 4,749,803; 4,793,886; 4,798,878; 4,874,805; 4,960,844; 4,978,706; 5,097,053; 5,272,224; 5,225,512; and 6,133,395 propose moisture-curable components that contain silane-terminated polyurethane for sealant and adhesives. These systems are stable in the absence of moisture. The incorporation of the silane groups into the sealants or adhesives is accomplished through silane-containing acrylic monomers, amino-silanes, chain transfer agents, isocyanate-silanes and epoxy-silanes. The silane groups are hydrolyzed by the moisture in atmosphere first to form silanols and then the silanols react with polyol or undergo self-condensation to form polymers.
U.S. Pat. No. 4,508,889 proposes the addition of polyisocyanate into a mixture of an amino-silane and a hydroxyl-functional polyol to make a silane-containing isocyanate-terminated polyurethane. This polyurethane is a moisture-curable urethane that can be used as adhesives and coatings.
Isocyanate-free moisture cure polyurethane coatings have been discussed in the publication (JCT, 2000 74(932) 81-87). The silane end-capped polyurethane utilizes a polyol derived from soybean oil. This isocyanate-free moisture polyurethane cures rapidly at room temperature.
Although many different technologies have been proposed for silane moisture curable coatings for sealant, adhesive, and coating applications, none of the above taught combining the silane moisture curable technology with conventional air oxidative curing technology to make dual curable storage stable 1k binders for coatings.